Removable Storage

Removable storage has been around almost as long as the computer itself. Early removable storage was based on magnetic tape like that used by an audio cassette. Before that, some computers even used paper punch cardsto store information.

We've come a long way since the days of punch cards. New removable storage devices can store hundreds of megabytes (and even gigabytes) of data on a single disk, cassette, card or cartridge. There are several reasons why removable storage is useful: it’s commercial software, you can make back-up copies for storing software and information that you don't need to access constantly, it’s possible to transport data between two computers (e.g. copying information to give to someone else), you can secure information that you don't want anyone else to access.

Modern removable storage devices offer an incredible number of options, with storage capacities ranging from the 1.44 megabytes (MB) of a standard floppy to the upward of 700 gigabyte (GB) capacity of some portable drives. All of these devices fall into one of three categories: magnetic storage, optical storage, solid-state storage.

MAGNETIC

Floppy disc

The most common and enduring form of removable-storage technology is magneticstorage. For example, 1.44-MB floppy-disk drives using 3.5-inch diskettes have been around for about 15 years, and they are still found on many computers sold today. In most cases, removable magnetic storage uses a drive,which is a mechanical device that connects to the computer. You insert the media,which is the part that actually stores the information, into the drive.

Just like a hard drive, the media used in removable magnetic-storage devices is coated with iron oxide.A disk is made from a thin piece of plastic coated with magnetic material on both sides. On the disk there are tracks. The tracks are arranged in concentric ringsso the software can jump from "file 1" to "file 19" without having to fast forward through files 2 through 18. The disk spins like a record and the heads move to the correct track, providing what is known as direct-access storage.

The read/write heads ("writing" is saving new information to the storage media) do not touch the media when the heads are traveling between tracks. There is normally some type of mechanism that you can set to protect a disk from being written to.

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